A body fat mass is recently being given attention as one index for knowing a health condition of a subject. In particular, a visceral fat mass is given attention as an index for making determination on whether or not a visceral fat obesity is present. The visceral obesity is said to induce lifestyle-related diseases that easily causes arterial sclerosis such as diabetes, a high blood pressure and hyperlipemia, and the use of the above index is expected from a standpoint of preventing such diseases. In this case, the visceral fat is a fat that accumulates around internal organs on an inner side of an abdominal muscle, and is distinguished from a subcutaneous fat that accumulates on a surface layer of the abdomen. An area (hereinafter referred to as visceral fat area) occupied by the visceral fat at a cross section of the abdomen of a portion corresponding to an umbilicus position is generally adopted for the index indicating the visceral fat mass.
Normally, an image analyzing method using a tomographic image of the abdomen photographed using an X-ray CT (Computer Tomography) or an MRI (Magnetic Resonance Imaging) is used to measure the visceral fat mass. In such an image analyzing method, the visceral fat area is calculated from the acquired tomographic image of the abdomen. However, in order to use such a method, a large facility that may be installed in medical institutions such as the X-ray CT and the MRI is required, and thus the visceral fat mass is very difficult to measure on a daily basis. A problem of exposure also arises when the X-ray CT is used, and thus such a method may not necessarily be a preferable measurement method.
As a measurement method taking the place thereof, application of a bioelectrical impedance method is being reviewed. The bioelectrical impedance method is a method of measuring the body fat mass widely used in a body fat measurement device for domestic use, where electrodes are brought into contact with four limbs, and the bioelectrical impedance is measured using such electrodes to calculate the body fat mass from the measured bioelectrical impedance. The above-described body fat measurement device accurately measures a degree of accumulation of the body fat by sites of the body such as the entire body or four limbs, or the body (trunk of the body), and is widely used in households and the like.
However, the conventional body fat measurement device measures the degree of accumulation of the body fat by sites of the body such as the entire body or four limbs, or the body (trunk of the body) as described above, and does not individually extract and accurately measure the degree of accumulation of the visceral fat or the degree of accumulation and the subcutaneous fat. This is because the body includes not only the visceral fat but also the subcutaneous fat, as described above, and thus accurately measuring the visceral fat mass and the subcutaneous fat mass individually is difficult in the body fat measurement device described above.
In order to solve such problems, consideration is being made of bringing an electrode directly in contact with the body, measuring the bioelectrical impedance using the electrode, and accurately measuring the visceral fat mass and the subcutaneous fat mass individually based thereon. For instance, Japanese Unexamined Patent Publication No. 2002-369806 (Patent Document 1) discloses a body fat measurement device configured such that the electrode is arranged in contact with the body by arranging an electrode on an inner peripheral surface of a belt member and wrapping and fixing the belt member to the body. The body fat measurement device disclosed in Japanese Unexamined Patent Publication No. 2002-369806 enables highly accurate measurement of the visceral fat mass and the subcutaneous fat mass, which has been difficult in the related art, by measuring the bioelectrical impedance using the electrode arranged in contact with the body of the subject using the belt member.
Patent Document 1: Japanese Unexamined Patent Publication No. 2002-369806